This disclosure relates to handheld nozzles connected to a fire hose. Firefighters often use this type of nozzle to extinguish fires in situations such as homes, cars, flammable liquid spills, and commercial properties where critical flow rates of at least 95 GPM (360 L/min) and pump pressures of at least 100 PSI (7 bar) are needed to overcome the fire. These nozzles develop reaction force of at least 50 lbf (23 kg) as a result of accelerating the water to velocities need for projecting fluids such as water acceptable distances and to form droplets into effective sizes. It's not uncommon for the reaction force to exceed half the weight of a firefighter. The physical limits of firefighters are oftentimes stretched to their maximum in the few moments a heavily laden firefighter with air pack rushes up many flights of stairs to rescue victims, setup firefighting equipment, and battle the blaze in incredibly hot rooms with near zero visibility conditions.
Added to that are forces from typical 1¾″ (45 mm) diameter hose filled with water, and the associated stiffness which increase the effort of restraining the nozzle to direct the trajectory in the desired direction. One hand has traditionally been dedicated towards this task, while a second hand is used to open and close the valve feeding water to the nozzle, leaving no hands free to help stabilize the fireman, drag hose, or tend to a hundred other tasks which might prove beneficial.
Dedicating a second hand to operating a valve handle has been the expectation given that the force to move lever operated valve handles is fairly high owing to the large frictions and forces resulting from high fluid pressure. For example National Fire Protection Association standard NFPA 1963, 2013 edition requires valve lever operating forces between 3 lbf (13.4 N) to 16 lbf (71.2 N) per section 4.6.3. Prior to institution of this standard it was not uncommon for valve handle levers to operate with at least 40 pounds pull.
Trigger operated nozzles are those whose valve is operated by a gripping force of the fingers. It's not uncommon to see nozzles of this type used for purposes such as use from a garden hose, for agricultural irrigation, chemical spraying (including pesticides and herbicides), paint spraying, or wash-down. This type of valve allows one to use a single hand to hold and operate the nozzle, and allows the flow to quickly turn on, and for the valve to shut off quickly by itself.
Triggers are not used to move a traditional valve on a firefighting nozzle. Lever handles on firefighting nozzles generally move along an arc distance of about 8 inches (20 cm) while a comfortable finger grip motion distance for a trigger is not even a fourth of that. Therefore an ordinary firefighting valve simply fitted with a trigger instead of a lever would have at least four times higher operating force. Finger muscles on this trigger would therefore be required to produce over four times as much force as the more powerful arm and shoulder muscles moving a lever. Inherently, this approach sounds unworkable.
Trigger operated nozzles are commonplace in small firefighting hoses at far lower flows, which is to say 1″ diameter hose (25 mm) and flows 60 GPM (240 L/min) or less. Trigger valves of a wide variety lend themselves to these conditions because a person's strength far exceeds operational forces encountered making trigger valves acceptable from an ergonomics standpoint.
Trigger valves lend themselves to the rapid valve on/off pulsing techniques found to be beneficial in controlling the atmosphere of rooms filled with un-ignited highly flammable superheated combustion byproducts, but up until now these nozzles were produced with maximum flows generally considered to be too small for safe structural (residential and commercial) firefighting. This technique is sometimes referred to flashover pulsing.
However, up until now larger sized trigger valves have not been commercialized for firefighting (larger, as described in the opening paragraphs) because of various obstacles to scaling up their size which made their use unacceptable, including reasons such as;                Fingers don't produce enough force to comfortably open a substantially larger valve element because fluid pressure acting on larger areas results in larger forces.        Frictional forces and seal drag caused by preload and fluid pressure to move larger valve elements make it difficult for fingers to operate the trigger.        Once opened, significant closing forces are often generated by fluid pressure and dynamic velocity in valve types used on small trigger nozzles. These forces while insignificant in smaller valves can become untenable if scaled up to larger valve sizes making it difficult for fingers to retain the valve in an open position.        Engaging a locking device to retain a valve in a flowing position generally cancels the safety benefits of a self-closing valve in the event of loss of grip on the nozzle. An unrestrained garden hose nozzle carries little risk of injury, whereas a 1¾″ hose whipping at 50 MPH can kill nearby people.        Trigger valves typically shutoff in an instant which is OK for small trigger nozzles, but becomes detrimental with larger sizes as nearly instantaneous deceleration of a large water mass produces significant water hammer which carries risks such as injury from catastrophic hose rupture, loss of extinguishing or protective flow, and the physical stress of sudden impulse change.        Physical size and weight of the nozzle would become unacceptably large if smaller trigger valves were simply scaled up.        Scaling up a small valve scales up the stroke needed to achieve a reasonable flow which also scales up the distance required operate a trigger to where it becomes larger than the grip capacity of a typical person's fingers.        Trigger valves generally are arranged so that the liquid enters the nozzle from the bottom and undergoes a direction change as it passes thru the front of the nozzle, thus the nozzle trajectory is neither parallel nor co-linear with the hose feeding it. As a result the hose is not positioned to absorb significant portions of the nozzle reaction force.        
Prior nozzles employing hydraulic control circuits such as disclosed in U.S. Pat. No. 5,261,494 to McLoughlin et. al. (the disclosure of which is incorporated herein by reference) move sliding valve elements between open and closed positions using chambers of water opened and closed by trigger position. However these valves have no positive mechanical engagement between trigger and sliding element so the position of the sliding element with respect to the trigger is subject to some uncertainty. For example; one could expect the valve to be fully closed at the start of a fire based on trigger position, only to find the valve element stuck open from lack of lubrication, corrosion, or from water supplies to the hose being terminated with the trigger depressed. Furthermore, water in hydraulic control circuits is subject to freezing in cold temperatures thus disabling the valve sooner than freezing occur in the full diameter of the waterway of a mechanically operated valve. Although springs added to the moving element could improve uncertainty somewhat, prudent safety practices would discourage use of hydraulically controlled trigger valves.
All of the prior firefighting nozzles will exhibit at least one of the drawbacks described above if scaled up. Moreover, all of the commercially available trigger operated firefighting nozzles have the water enter the bottom of the nozzle, at a significant angle to the discharge line of action.
Lever handle slide valves have found widespread use in the field because of the ease of which the handle may be operated, and the relative lack of turbulence. Attempts to move slide valves of this type by a straight linear pull, or by using a simple lever with a pivot point have resulted in valves with substantial risk of water hammer, and relatively high forces on the slider making them difficult to open with finder pull, and susceptible to self-opening or closing tendencies at various flows and pressures. A new mechanism therefore is needed.